A startling new study reveals that long-duration spaceflight literally softens astronauts’ eyes, with potential implications for future deep space missions to Mars. Research from the Université de Montréal found that astronauts’ eyes become significantly less rigid after spending six months aboard the International Space Station (ISS).
At least 70 percent of ISS astronauts have experienced vision changes in space, a condition known as spaceflight-associated neuro-ocular syndrome (SANS). Now, researchers have identified specific mechanical changes in the eye that may explain why.
“Weightlessness alters the distribution of blood in the body, increasing blood flow to the head and slowing venous circulation in the eye,” explained Santiago Costantino, who led the research at Université de Montréal’s Maisonneuve-Rosemont Hospital.
The study, published in the Journal of Engineering in Medicine and Biology, analyzed data from 13 astronauts who spent between 157 and 186 days on the ISS. The diverse group included crew members from American, European, Japanese and Canadian space agencies, with an average age of 48. Eight were first-time space travelers, and 31 percent were women.
Using advanced imaging techniques, the researchers measured three key properties of the astronauts’ eyes before and after their missions. The results were dramatic: eye rigidity decreased by 33 percent, internal eye pressure dropped by 11 percent, and the pulse of blood flow through the eye diminished by 25 percent.
These changes manifested in various symptoms, including altered eye shape, changes in visual focus, and in some cases, swelling of the optic nerve and retinal folds. Five astronauts also showed unusual thickening of the choroid – the eye’s vascular layer that nourishes the retina.
The research team believes that the expansion of blood vessels in the eye during weightlessness may stretch the eye’s outer white layer, called the sclera, leading to lasting changes in the eye’s mechanical properties. They also suggest that blood flow changes in zero gravity could create a “water-hammer effect,” where sudden pressure changes shock the eye tissue, causing significant remodeling.
For current six-to-twelve-month ISS missions, these changes aren’t typically cause for alarm. While 80 percent of the studied astronauts developed at least one symptom, their eyes returned to normal after returning to Earth. Most cases were adequately managed with corrective eyeglasses during their space stay.
However, the findings raise serious questions about longer missions, such as a potential journey to Mars. “The eye-health effects of prolonged exposure to microgravity remain unknown, and no preventive or palliative measures now exist,” Costantino noted.
The research could help identify astronauts at risk before they develop serious eye problems during extended missions. “The observed changes in the mechanical properties of the eye could serve as biomarkers to predict the development of SANS,” said Costantino.
The Maisonneuve-Rosemont research team is now awaiting additional data from NASA to continue their investigations, which could prove crucial for protecting astronaut vision during humanity’s next giant leap into deep space.